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(No Model.) 2 SheetsSheet 1. G. M. S'EARLE & G. N. SAEGMULLER.

RANGE FINDER.

No. 588,094. Patented Au 10,1897.

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ATTORNEYS.

(No Model.) 2 She'et-sSheet 2.

No. 588,094. Patented Aug. 10,1897.

WITNESSES. INVENTORY: a M 0&07196 JIZ. Se r-fi Geozzge .17! Gas Mullen61M I By W M ATTORNEYS.

UNITED! STATES PATENT OFFICE.

GEORGE M. SEAR-LE AND GEORGE N. SAEGMULLER, OF \VASHINGTON, DISTRICT OFCOLUMBIA.

RANGE-FINDER.

SPECIFICATION forming part of Letters Patent No. 588,094, dated August10,1897.

Application filed April 12, 1897. Serial No. 631,756. (No model.)

To all whom it may concern:

Be it known that we, GEORGE M. SEARLE and GEORGE N. SAEGMULLER,OfWashington, in the District of Columbia, have invented a new and usefulImprovement in Range-Finders, of which the following is a specification,

The object of our invention is to provide an improved range-finder foruse in measuring the distance of remote objects (such, for instance, asan enemys vessel at sea) and indicating the said distance at once on ascale without calculation. In another application of even date herewith,marked Case A, we have shown and described an instrument for the samepurpose embodying somewhatsimilar principles.

The present improvement is intended to meet the requirement of measuringthe distance from an observation-point aloft on the masthead and isorganized to adapt it to use in this location.

It consists in the construction and arrangement of the parts of theinstrument hereinafter shown and described, reference being had to theaccompanying drawings,in which-- Figure 1 is a side elevation,partly insection; Fig. 2, a front elevation in section through line 2 2 of Fig.1, looking in the direction of the arrow. Fig. 2 is an enlargedhorizontal section on line 2 2 of Fig. 1, showing the internalarrangement of the eyepiece of the telescope. Fig. 2 is a side view ofthe same parts. Fig. 3 is a diagram of the prisms and telescope; Fig. 4,a diagram of the adjustable refractingplate for bringing the images into coincidence, shown in connection with the cotangent scale.

In the drawings, Figs. 1 and 2, X represents a tube from six to ten feetlong and forming the base-line. This tube stands vertically and is hungabout its middle upon a post or pillar Y, so that it may be carried onthe platform at the masthead. In the top and bottom portions of the tubeare lateral openings in which are set reflecting-prisms A and B, (ormirrors,) each adapted to receive the incident ray and send out theemergent ray at right angles to each other in a downward direction. \Veprefer for this purpose a double reflecting-prism, as shown in Fig. 3,for the reason that slight variation in its position does not interferewith the proper alinement of the emergent ray. These two prisms arearranged (see Fig. 2) in dilierent planes so that the rays from a remoteobject falling on one will be reflected to one-half of the object-glassof a telescope 25, while the rays from the other will be thrown upon theother half of the objectglass without interference with each other. Thetelescope is fixed to the base-line tube X at one end in alinement withthe same, and the eyepiece is on the side of the telescope, so that thedirection of sight will be parallel to the incident rays on the prisms AB.

Referring now to the diagram Fig. 3, two pencils of rays P P Q Q,proceeding from an object too far away to be represented in the figure,fall on the two prisms A and B. These prisms, being doubly reflectingwith reflecting-surfaces a a and b b, at making an angle of forty-fivedegrees with a and b with I), send the pencils out at the faces a and d,respectively, each ray being at an angle equal to ninety degrees fromthe original direction at which it left the object. These rays enter theobject-glass 0 of a telescope i and proceed to a diagonalreflecting-prism p, (or mirror,) placed near the eyepiece, formingimages z'j in the field of the eyepiece. As these pencils consist,sensibly or practically, of parallel 'rays, (the prisms being very smallcompared with the distance,) the images i j will be separated by adistance having the same ratio to the focal length of the telescope thatthe distance between corresponding parts of the prisms A B has to thedistance fromeither to the object.

The object now to be accomplished is the measurement of the distance 2'j, which varies reciprocally as the distance of the object observed.This can be done as follows: In the path of the pencil coming throughone of the prisms-say ]3'a plate of glass g, Fig. at, is interposedafter or before it strikes the prism 17. This plate has parallel sides,and its effeet is to transfer laterally the axis of the pen- 5 ICCfield. This inclination Varies with approximate uniformity to produce auniform change in the distance by which the image is transferred, sothat. the amount of angular movement of the plate from a positionperpendicular to the rays is approximately inversely proportional to thedistance of the object observed, since this distance is to the base asthe focal length of telescope is to the angular movement of the plate orangular movement: base focal length distance of object inverse orreciprocal of an angle is approximately its cotangent, so that if C bethe center around which the plate turns or revolves,

, approximately. Now the ,C F the prolongation of its plane, C G theposition of no inclination or transference when the ray strikes theplate perpendicularly and passes through undisturbed, and O E theperpendicular to C G, then the distance E F is proportional to thecotangent of the angle F C G or the inclination. A scale approximatelyof equal parts (which can be accurately computed by mathematicalformulas if the thickness and index of refraction of the plate, thefocal length of the telescope, and the length of the base are known) canthere fore be laid off on E H, and on this scale a pointer fixed to andmoving with plate g will give the distance of the object by turning theplate 9 until coincidence of the two images has been produced.

As shown in Figs. 2 and 2 this refractingplate or coincidence-plate g isprovided with its pointer g operating across the cotangent scale E H.This pointer g is fixed to a wormwheel 9 and both are rigid with theaxial rock-shaft that carries the glass plate 9, and

scale is that it practically gives the indications in equal partsirrespective of the distance of the object, and this is an importantadvantage, since without it the readings of the scale would get closertogether as the distance of the object increased, for the greater thedistance of the object in proportion to the base-line the closer the twoimages on the object-glass would appear, and hence a continually-smallerdeflection of the plate g would be required which for long distanceswould j umble the graduations and figures together, so that theywouldnot be easily legible. By the cotangent scale a continually-increasedmeasurement on the line E H is made for each successive equal movementof the plate g about its axis, so as to compensate for this crowd ing ofthe markings, and thus render the scale practically one of equal parts.

Having thus described our invention, what we claim as new, and desire tosecure by Letters Patent, is-

A range-finder comprisinga telescope, two reflecting-prisms separated,in fixed relation, a distance apart representing a base-line andarranged in different planes so that each sends its own rays upon adifferent portion of the object-glass of the telescope, anaxially-adjustable retracting-plate for receiving the rays from one ofthe reflecting -prisms and bringing them into coincidence with the other

